Long wavelength signal enhancement for contact magnetic transfer recording

ABSTRACT

A master and a copy tape are placed in slippage-free contact and the copy tape is sensitized to receive the magnetic signals from the master tape. A bar having high permeability and generally conforming to the magnetic lines of force from the master tape is placed closely adjacent the copy tape to increase the field intensity of the long wavelength magnetic signals through the copy tape.

[76] Inventor:

United States Patent [1 1 Smaller LONG WAVELENGTH SIGNAL ENHANCEMENT FOR CONTACT MAGNETIC TRANSFER RECORDING Philip Smaller, 4155 Wilkie, Palo Alto, Calif. 94306 [22] Filed: Oct. 28, 1971 [21] Appl. No.: 193,451

[52] US. Cl 179/1002 E, 179/1002 C [51] Int. Cl. Gllb 5/86 [58] Field of Search 179/1002 E, 100.2 C,

179/1002 D, 100.2 CF; 346/74 MP, 74 MT; 235/61.l2 M; 340/l74.1 F

[56] References Cited UNITED STATES PATENTS 3,373,416 3/1968 Geurst et a1. 179/1002 C 3,371,164 2/1968 Makimura 179/1002 C 3,432,838 3/1969 Wikler 179/1002 C 3,152,225 10/1964 Peters 179/1002 C 2,738,383 Herr et a1 179/1002 E Aug. 14, 1973 2,795,651 6/1957 Camras 179/1002 E 2,747,026 5/1956 Camras 179/1002 E 3,573,390 4/1971 Frost 179/1002 E 2,918,537 12/1959 Camras 179/1002 E 2,926,219 2/1-960 Hollmann 179/1002 E 3,037,090 5/1962 Bouzemburg '179/1002 E 3,277,244 10/1966 Frost 179/1002 E Primary Examiner-Hemard Konick Assistant Examiner-Alfred H. Eddleman Attorney-Charles M. Hogan et al.

[5 7] ABSTRACT A master and a copy tape are placed in slippage-free contact and the copy tape is sensitized to receive the magnetic signals from the master tape. A bar having high permeability and generally conforming to the magnetic lines of force from the master tape is placed closely adjacent the copy tape to increase the field intensity of the long wavelength magnetic signals through the copy tape.

9 Claims, 4 Drawing Figures Patented Aug. 14, 1973 UOKDOw LONG WAVELENGTH S1GNAL ENHANCEMENT FOR CONTACT MAGNETIC TRANSFER RECORDING The present invention relates to magnetic recording and more particularly to direct contact transfer record- In recent years the direct contact method of transfer recording has been proposed to economically and rapidly transfer magnetic signals from a master to a copy tape.

Briefly, this approach involves placing the master and copy tapes in slippage-free contact while the copy tape is sensitized to receive and retain the magnetic signals from the master tape. The copy tape is sensitized either by biasing it magnetically or by placing it in a paramagnetic state where it is easily magnetized by the signals of the master tape.

.Both of these methods have a common problem. This problem is the inefficient transfer of long wavelength magnetic signals relative to the mid-wavelength range. Long wavelength" is taken to be wavelengths in excess of X 10- inches, mid-wavelength from 1.0 X 10' inches to 10 X 10 inches, and short wavelengths are less than 1.0 X 10 inches. Various steps have been taken to solve this problem of inefficient transfer. Examples may be found in patent application Ser. No. 185,225, now U.S. Pat. No. 3,699,269, entitled Improved Double Transfer Tape Copy System, and patent application Ser. No. 185,136, now U.S. Pat. No. 3,725,611, entitled Double Coated Storage Medium for Contact Transfer Recording", both of common inventorship with the present invention.

There is one problem that remains to be solved. This is the fact that the magnetic field of the signals emanates in both directions from the master tape so that one half of the field associated with the signal is not used. The problem is not so critical for the midwavelength signals since' they are efficiently transferred and the reduction in magnetic intensity is not critical. With the long wavelength signals, however, the reduction of magnetic intensity, due to non-used magnetic force lines, as well as the theoretical decrease in intensity with increasing wavelength, substantially reduces the effectiveness of the transfer of this type of signal.

Accordingly, it is an object of the present invention to enhance in a process of the above general type the transfer of long wavelength magnetic signals.

This end is achieved by concentrating the long wavelength magnetic field emanating from a master magnetic storage medium in slippage-free contact with a copy storage medium through a high permeability magnetic material in close proximity to the copy storage medium.

The above and other related objects and features of the present invention will be apparent from a reading of the description of the disclosure shown in the accompanying drawing and the novelty thereof pointed out in the appended claims.

In the drawing: 1

FIG. 1 shows a direct contact transfer bodying the present invention;

FIG. 2 illustrates the magnetic line of force for a prior art direct contact transfer process;

FIG. 3 illustrates the magnetic lines of force for a direct contact transfer process embodying the present invention;

process em- FIG. 4 illustrates an alternate embodiment of the direct contact transfer process of FIG. 3.

The drawing shows a master tape generally indicated by reference character 10, comprised of a flexible nonmagnetic base 12 and a ferromagnetic layer 14 containing magnetic signals. A copy tape 16 having a flexible base 18 and ferromagnetic layer 20 is placed in slippage-free contact with the master tape 10 by a suitable arrangement, such as guide plates 22 and 24. It should be apparent to those skilled in the art that the tapes may be placed in slippage-free contact by a number of equivalent arrangements.

During the contact period the copy tape 16 is made sensitive to the signals on the master tape 10 by a number of methods. One such method and the one shown herein comprises the use of a magnetic head 26 for magnetically biasing the copy tape 16 while in contact with the master 10. It should be pointed out that this approach requires a master tape having a higher coercivity than the copy tape. in addition, the magnetic bias should not be so great that it would erase the signals on the ferrite layer 14 of master tape 10. Other methods also may be used to sensitize the copy tape. One example is selecting a copy tape with a relatively low Curie point and with a reasonably high room temperature coercivity, such as chromium dioxide. In this method the low Curie point material is heated to a paramagnetic state prior to contact with the master tape so that the copy tape is easily saturated by the magnetic signals on a the master tape. During the contact period the copy tape cools to a ferromagnetic state where the strength of the magnetic signals increases.

' During the contact transfer the short wavelength signals are efficiently transferred. However, the long wavelength signals have fields extending on both sides of the tape. To minimize if not eliminate this, a concentrator, generally indicated by reference character 28, is placed in close proximity to the copy tape 16. The concentrator 28 may be in the form of an arcuate. bar of high permeability soft magnetic material, such as soft iron or Permalloy, available from Magnetic Metals Co., Camden, NJ. This concentrator tends to collect the lines of magnetic force emanating from a dipole L, as sociated with a long wavelength signal, that would otherwise extend on the opposite side of the tape. It is obvious that the concentrator 28 may have a predetermined configuration to provide the maximum concentration of the long wavelength signals. The collector 28 is shaped to conform generally to the magnetic lines of force emanating from the master tape so it more effectively concentrates those signals through the ferromagnetic layer 20 of the copy tape 16. In addition, the edge 32 of the bar 28 closest to the copy tape 16 tends to further concentrate the magnetic lines of flux to increase the field intensity. This results in a greatly improved transfer of the long wavelength signals. FIGS. 2 and 3 illustrate the magnetic field lines of force before and after a straight bar concentrator 30 is used. The field intensity at the trailing edge 32 of the concentrator 30 is enhanced by this means. Edge 32 is more important than edge 34 (away from the tape 16) because with the tape moving from left to right edge 32 acts on the tape last.

1n the case of magnetic bias it is possible to supply the bias field by other methods than the magnetic head 26. In some cases an air solenoid with no magnetic material is useful. An alternative method is to use the bar 28 as a source of the bias. FIG. 4 shows a coil 36 wound on bar 30 and an AC. source 38 used to excite the coil. This method has the definite advantage that the strongest bias field occurs at the same point in the copy tape where the signal field from the master is strongest. This condition will guarantee the most efficient signal transfer.

While the preferred embodiment of the present invention has been described, it should be apparent to those skilled in the art that the invention may be practiced in other forms without departing from the spirit and scope of the present invention.

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. Apparatus for direct contact transfer of magnetic signals from a master magnetic storage medium to a copy storage medium, the master magnetic storage medium having a spectrum of signals including short and long wavelength signals, each producing a distinct pattern of magnetic lines of force emanating from the master magnetic storage medium, said apparatus comprising:

means for placing said master and copy storage medium in slippage-free contact while both are in motion;

a concentrator comprised of high-permeability magnetic material in close proximity to said copy storage medium, said concentrator being shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals on said master magnetic medium, whereby the magnetic lines of force produced by the long wavelength signals on said master magnetic storage medium are concentrated through said copy storage medium; and

means for increasing the sensitivitY of said copy storage medium to the magnetic signals on said master storage medium for transferring both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.

2. Apparatus as in claim 1 wherein said tapes move in a given direction, said concentrator is in the form of a bar having one edge closely adjacent the copy storage medium.

3. Apparatus as in claim 1 wherein said concentrator is comprised of an arcuate bar extending generally along the magnetic field lines emanating from the long wavelength signals on said master magnetic storage medium.

4. A method of enhancing the direct contact transfer of long wavelength magnetic signals comprising the steps of:

placing a master magnetic storage medium having magnetic signals on it in slippage-free contact with a copy magnetic storage medium;

simultaneously concentrating the magnetic lines of force produced by the long wavelength signals through the copy storage medium with a concen- 6 simultaneously sensitizing the copy storage medium so that the magnetic field emanating from the master magnetic storage medium magnetizes the copy storage medium to transfer both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.

5. A method as in claim 4 wherein said long wavelength magnetic signals are concentrated by a soft magnetic material having a shape which conforms generally to the lines of force emanating from the master magnetic storage medium and having edges at either end closely adjacent said copy storage medium.

6. A method as in claim 4 wherein said copy storage medium is sensitized by magnetically biasing it.

7. Apparatus for direct contact transfer of magnetic signals from a master magnetic storage medium to a copy storage medium, the master magnetic storage medium having a spectrum ofsignals including short and long wavelength signals, each producing a distinct pattern of magnetic lines of force emanating from the master magnetic storage medium, said apparatus comprising:

means for placing said master and copy storage medium in slippage-free contact while both are in motion in a given direction;

a concentrator comprised of high'permeability magnetic material having a trailing edge relative to the direction of motion of said master and copy storage mediums, said trailing edge being in close proximity to said copy storage medium, said concentrator being shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals on said master magnetic medium, whereby the magnetic lines of force produced by the long wavelength signals on said master magnetic storage medium are concentrated through said copy storage medium; and

means for increasing the sensitivity of said copy storage medium to the magnetic signals on said master storage medium for transferring both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.

8. Apparatus as in claim 7 wherein said master magnetic storage medium has a higher coercivity than said copy storage medium, and wherein said apparatus further comprises a coil of wire positioned around said concentrator and adapted to be supplied with electric current whereby said concentrator increases the sensitivity of said copy storage medium by magnetic bias.

9. A method of enhancing the direct contact transfer of long wavelength magnetic signals comprising the steps of:

placing a master magnetic storage medium having magnetic signals on it in slippage-free contact with a copy magnetic storage medium;

moving saidstorage mediums in a given direction;

simultaneously concentrating the magnetic lines of simultaneously sensitizing the copy storage medium so that the magnetic field emanating from the master magnetic storage medium magnetizes the copy storage medium to transfer both short and long wavelength signals to said copy storage medium. the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness. 

1. Apparatus for direct contact transfer of magnetic signals from a master magnetic storage medium to a copy storage medium, the master magnetic storage medium having a spectrum of signals including short and long wavelength signals, each producing a distinct pattern of magnetic lines of force emanating from the master magnetic storage medium, said apparatus comprising: means for placing said master and copy storage medium in slippage-free contact while both are in motion; a concentrator comprised of high-permeability magnetic material in close proximity to said copy storage medium, said concentrator being shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals on said master magnetic medium, whereby the magnetic lines of force produced by the long wavelength signals on said master magnetic storage medium are concentrated through said copy storage medium; and means for increasing the sensitivitY of said copy storage medium to the magnetic signals on said master storage medium for transferring both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.
 2. Apparatus as in claim 1 wherein said tapes move in a given direction, said concentrator is in the form of a bar having one edge closely adjacent the copy storage medium.
 3. Apparatus as in claim 1 wherein said concentrator is comprised of an arcuate bar extending generally along the magnetic field lines emanating from the long wavelength signals on said master magnetic storage medium.
 4. A method of enhancing the direct contact transfer of long wavelength magnetic signals comprising the steps of: placing a master magnetic storage medium having magnetic signals on it in slippage-free contact with a copy magnetic storage medium; simultaneously concentrating the magnetic lines of force produced by the long wavelength signals through the copy storage medium with a concentrator shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals; simultaneously sensitizing the copy storage medium so that the magnetic field emanating from the master magnetic storage medium magnetizes the copy storage medium to transfer both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.
 5. A method as in claim 4 wherein said long wavelength magnetic signals are concentrated by a soft magnetic material having a shape which conforms generally to the lines of force emanating from the master magnetic storage medium and having edges at eiTher end closely adjacent said copy storage medium.
 6. A method as in claim 4 wherein said copy storage medium is sensitized by magnetically biasing it.
 7. Apparatus for direct contact transfer of magnetic signals from a master magnetic storage medium to a copy storage medium, the master magnetic storage medium having a spectrum of signals including short and long wavelength signals, each producing a distinct pattern of magnetic lines of force emanating from the master magnetic storage medium, said apparatus comprising: means for placing said master and copy storage medium in slippage-free contact while both are in motion in a given direction; a concentrator comprised of high-permeability magnetic material having a trailing edge relative to the direction of motion of said master and copy storage mediums, said trailing edge being in close proximity to said copy storage medium, said concentrator being shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals on said master magnetic medium, whereby the magnetic lines of force produced by the long wavelength signals on said master magnetic storage medium are concentrated through said copy storage medium; and means for increasing the sensitivity of said copy storage medium to the magnetic signals on said master storage medium for transferring both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness.
 8. Apparatus as in claim 7 wherein said master magnetic storage medium has a higher coercivity than said copy storage medium, and wherein said apparatus further comprises a coil of wire positioned around said concentrator and adapted to be supplied with electric current whereby said concentrator increases the sensitivity of said copy storage medium by magnetic bias.
 9. A method of enhancing the direct contact transfer of long wavelength magnetic signals comprising the steps of: placing a master magnetic storage medium having magnetic signals on it in slippage-free contact with a copy magnetic storage medium; moving said storage mediums in a given direction; simultaneously concentrating the magnetic lines of force produced by the long wavelength signals through the copy storage medium with a high-permeability concentrator shaped to conform generally to the pattern of the magnetic lines of force associated with the long wavelength signals and having a trailing edge relative to the direction of motion of said storage mediums, said trailing edge being in close proximity to said copy storage medium; and simultaneously sensitizing the copy storage medium so that the magnetic field emanating from the master magnetic storage medium magnetizes the copy storage medium to transfer both short and long wavelength signals to said copy storage medium, the concentration of the long wavelength magnetic lines of force through said concentrator resulting in the improved transfer of said long wavelength signals, thereby resulting in the transfer of both said long and short wavelength signals with substantially equal effectiveness. 